Semiconductor Memories

 Semiconductor memory is an electronic data storage device, often used as computer memory, implemented on a semiconductor-based integrated circuit. Introduction

Semiconductor memory

Example of Semiconductor memory  Examples of semiconductor memory includes Non-volatile memory such as Read-only memory (ROM), Magnetoresistive Random Access Memory (MRAM), and Flash memory.  It also includes volatile memory such as Static Random Access Memory (SRAM)

Cont.,  These memories can be constructed to store large amount of data entirely within a computer system.  The number of locations and the size of storing data may vary from memory to memory.  Each location is called Memory cell.

Memory cell operation

Memory cell  The memory cell is used to store single bit of information.  The memory cell is fabricated by using either bipolar Metal Oxide Semiconductors (MOS) or Complementary Metal Oxide Semiconductors (CMOS).

Semiconductor memory classification

Memory Architecture: Decoders

Array-Structured memory Architecture

Hierarchical memory Architecture

Memory Timing Definitions

Memory Timing Approaches

Read-Write Memories (RAM) Static (SRAM)  Data stored as long as supply is applied  Large (6 transistor/cell)  Fast  Differential

Read-Write Memories Dynamic (DRAM)  Periodic refresh required  Small (1-3 transistors/cell)  Slower  Single Ended

6- Transistor CMOS SRAM Cell

CMOS SRAM Analysis (Write)

CMOS SRAM Analysis (Read)

6T- SRAM - Layout V DD GND Q Q WL BL M1 M3 M4M2 M5M6

3- Transistor DRAM Cell

3-T DRAM Layout BL2BL1GND RWL WWL M3 M2 M1

DRAM Cell  1T DRAM requires a sense amplifier for each bit line, due to charge redistribution read-out.  DRAM Memory cells are single ended in contrast to SRAM cells.

1-T DRAM cell

Semiconductor Memory Trends Memory Size as a function of time: x 4 every three years

Semiconductor Memory Trends Increasing die size factor 1.5 per generation Combined with reducing cell size factor 2.6 per generation

Semiconductor Memory Trends Technology feature size for different SRAM generations

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